fix: --config flag now fully overrides ~/.strix/cli-config.json (#457)

* fix: --config flag now fully overrides ~/.strix/cli-config.json (fixes #377)

Previously, env vars applied from the default config at module import time
were not cleared when --config was later processed, causing settings from
~/.strix/cli-config.json to leak into runs that specified a custom config.

Track which vars were applied by the initial default-config load in
Config._applied_from_default. In apply_config_override, clear those vars
before applying the custom config so only the custom file's settings take effect.

* Add config override regression test

* Make config override test setup explicit

---------

Co-authored-by: octo-patch <octo-patch@github.com>
Co-authored-by: bearsyankees <bearsyankees@gmail.com>

strix/interface/main.py

@@ -6,6 +6,7 @@ Strix Agent Interface
 import argparse
 import asyncio
 import logging
+import os
 import shutil
 import sys
 from pathlib import Path
@@ -528,6 +529,12 @@ def pull_docker_image() -> None:
 
 
 def apply_config_override(config_path: str) -> None:
+    # Clear env vars that were automatically applied from the default config file
+    # so they don't leak into the custom config context.
+    for var_name in Config._applied_from_default:
+        os.environ.pop(var_name, None)
+    Config._applied_from_default = {}
+
     Config._config_file_override = validate_config_file(config_path)
     apply_saved_config(force=True)